Swift 2.0 Beta字典扩展

Question

Trying to create an immutable Dictionary. The idea is to have immutable arrays of keys and values each and then pass them to a

Dictionary constructor: let dict = Dictionary(aStringArray, aSameLengthDoubleArray)

The following code however gives a compile time error.

extension Dictionary {
    init<T:Hashable,U>(keys: [T], values: [U]) {
        self.init()
        for (index, key) in keys.enumerate() {
            self[key] = values[index]
        }
    }
}

Error:

error: cannot subscript a value of type 'Dictionary' with an index of type 'T' self[key] = values[index]

Can someone throw some light on this?

Answer 1

If you know that Dictionary already has typealiases for its associated types key and values. The keys should be of type Key and value should be of type Value . Just like you would have Element type in Array . The above thing you could achieve simply using Key and Value as so,

extension Dictionary {
    init(keys: [Key], values: [Value]) {
        self.init()
        for (index, key) in keys.enumerate() {
            self[key] = values[index]
        }
    }
}
let a = Dictionary(keys: [1, 2, 3, 4, 5], values: ["Michael", "Jack", "Kurt", "Jim", "Stewart"])